Total Phenolics and Phenolic Acids in Plants and Soils
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During allelopathic investigations of interrelationships among different plant species in their natural sites, special attention is paid to the presence of phenolic acids (PAs) in dominant plants, plant litter and in the soil. They are localized in all plant organs, both as free and in bound forms i.e. associated with other compounds such as lignin (Kögel and Bochter 1985; Kögel 1986) and polysaccharides of cell walls (Whitmare 1976). Phenols are transferred from plants to the litter and soil by foliage and stem leaching, leaf fall, root exudates, microbial decomposition of plants remains, (mainly the degradation of lignin). PAs have been identified as the main phytotoxins of some plant species (Lodhi and Rice 1971; Chou and Muller 1972). Phytotoxins play a significant role as germination inhibitors that affect growth of seedlings, soil nitrification and nitrifying bacteria (Lodhi and Killingbeck 1980, Einhellig et al.,1982, Khan and Ungar, 1986). This chapter describes the methods for extraction, detection and measurement of total phenolics and phenolic acids in dry plant material (vegetative plant parts, mostly leaves), plant litter and soil (organic and mineral); method of induced chlorophyll fluorescence kinetics of photosystem II for determination of photosynthetic efficiency; methods for chlorophyll content determination and methods of biotests.